A basic problem with residential and commercial plumbing systems is the back flow of sewage and drain water into the plumbing fixtures of a sewage generating facility due to a blockage or an obstruction of the sewer line. This problem is amplified where the sewage generating facility comprises an apartment building, an office building, or a similar multi-unit structure having a large number of drain fixtures therein. Hospitals, food handling or food service establishments and like structures are of particular concern because the back flow of any sewage into such facilities presents even greater opportunity for serious health hazards. In order to provide access to such blockages and obstructions, plumbing codes require commercial and residential plumbing systems to include sewer cleanouts throughout the system, both within the sewage generating facility and between the sewage generating facility and a sewage collection facility. Typically, a sewer cleanout comprises a threadably sealed plug secured to the uppermost portion of a T-fitting in the sewer line. When a blockage of the sewer lines occurs, access, thereto is provided by removing the plug. However, because the typical sewer cleanout is only intended to provide access to a sewer line, it is not designed to solve the more immediate problem of preventing the back flow of sewage into the drain fixtures of the sewage generating facility.
Various devices are known in the prior art purporting to solve this problem. Devices have been provided as shown in U.S. Pat. No. 4,261,386, wherein a cap is removably secured to the uppermost portion of a conventional T-fitting. As sewage enters the shank of the T-fitting, the air pressure therein will increase. When sufficient pressure has accumulated, the cap is forceably ejected from the fitting and the sewage escapes the system through the opening in the top of the shank.
Problems exist, however, with such prior art devices. For example, a plumbing system will commonly sustain minor blockages of a sewer line. These blockages are often purged from the sewer line by the increased pressure which results from normal use of the system. A plumbing system therefore experiences normal pressure fluctuations due to minor blockages. Should the cap of the patented device be ejected by such pressure fluctuations, the device becomes an open vent for sewer gas because the cap does not automatically reclose. Furthermore, undesired foreign material such as rocks, sticks, garbage, subsurface water and rats, is thereby permitted to enter the system. Another problem with the patented device is that the cap is retained to the T-fitting solely by means of friction fitting gaskets. Such retention means are widely known to become undependable over time. A yet further problem is that no prior art device, including the patented sewer relief valve, is tamper-resistant. Such a feature is required by most plumbing codes throughout the United States. Thus, it is not surprising that such prior art devices are not widely used in the plumbing industry.
Another prior art device which purports to solve the basic problem of preventing the back flow of sewage into a sewage generating facility is a back water valve. Placed betweeen a sewage generating facility and a sewage collection facility, the typical back water valve includes a hinged door or swing gate which opens in the direction of normal sewage flow. In theory, a back flow of sewage closes the gate, thereby preventing any back flow into the sewage generating facility.
Although back water valves are widely used and often required by code, several problems persist. A back water valve functions only to stop sewage flowing from a sewage collection facility to a sewage generating facility. It does not prevent the sewage generating facility from being subjected to its own back flow of sewage which results after the valve has closed due to a back flow of sewage from the sewage collection facility. Furthermore, back water valves are recognized to be only partially effective because they obstruct sewage flow and collect foreign matter. Such a collection of foreign matter inhibits the valve's ability to function and, therefore, the back water valve itself becomes an obstruction of the sewer line.